The present invention relates to an integral joint of two pipes.
More specifically, the present invention relates to an integral joint system for pipes to be used as a well casing.
The term xe2x80x9ccasingxe2x80x9d, as used in the present description and claims, refers to a tubular structure, consisting of various portions of pipe assembled together by means of a mechanical joint, set inside a well for the production of hydrocarbons as reinforcement and support of the walls of the well itself.
As it is known, the petroleum industry has the tendency of reducing the diameters of production wells to obtain a reduction in the drilling costs. To achieve this result, however, the connections which join the portions of pipe to obtain the casing, must have a geometry which is substantially identical to that of the pipes themselves, i.e. substantially having the same external and internal diameter.
Integral connections or joints, such as flush joints and near-flush joints, have been proposed for the purpose, which have an external diameter equal to that of the pipes to be assembled (flush joint) or a slightly higher diameter (2-3.5%) (near-flush joint).
The disadvantage of these joints, however, is the supplying of connections with mechanical properties, such as tensile, compression, torque and bending strengths which are much lower than those of the pipes themselves. In particular, the tensile strength of flush joints or near-flush joints vary from 65% to 75%, with respect to the pipe body, depending on the diameter and thickness of the pipe. The compression, bending and torque strengths, which are often a fraction of those of the pipe, are even more reduced.
These reductions in the mechanical characteristics limit the applications of these connections to wells with a limited depth, with low differential pressures and which do not require rotation while inserting the pipe inside the drilling holes (as required for example in the case of liner cementation).
Integral, near-flush joints of the type mentioned above, containing modifications suitable for improving the mechanical characteristics, have been proposed in literature with the aim of overcoming these drawbacks. For example, the published international patent application WO 93/18329 describes an integral joint, machined on each end of the pipes to be assembled, made up of two elements, pin and box. Each element contains at least two threaded sections each separated by a joining shoulder suitable for mating into each other when the pipes are assembled.
The published European patent application 767,335 describes an integral joint for pipes, machined on each end of the pipes to be assembled and made up of two threaded elements, pin and box, having a tapered-conical longitudinal section. The two threads are interrupted, in an intermediate position, by a shoulder orthogonal to the axis of the pipes.
To improve the sealing effect of the joint, the initial parts of the threads of the pin element and the end parts of the threads of the box element have been removed, by mechanical processing, so that, when joined, the two surfaces come into contact with a consequent elastic deformation of the surfaces involved.
The connections described above, although having improved mechanical performances with respect to a flush type joint, are still not sufficient to guarantee suitability for deep wells.
The Applicant has now found an integral joint, of the near-flush type, characterized by a significant improvement in the compression and torque strengths. This improvement is obtained by means of a particular design of the ends of the pin and box elements of the joint, as described hereunder, which allows the machining of at least two shoulders (external and intermediate), in order to increase the compression strength to a value close to the tensile strength and also the torque strength, whose maximum value is equal to about 2.5 times the make-up torque of the joint.
In addition, the presence of two metal seals (internal and external), together with the shoulders and particular two-step thread profile, allows the connection to have an excellent resistance to combined load, making it possible to tolerate extreme pressure, tensile, compression, bending and torque stresses in the well, making the connection itself very appropriate for deviated or horizontal, high pressure and high temperature wells.
The object of the present invention therefore relates to an integral joint for the connection of two pipes comprising:
a) a first box element with a tapered-conical longitudinal section, equipped with an internal two-step thread machined at an end of a first pipe;
b) a second pin element, equipped with an external two-step thread machined at an end of a second pipe, having a tapered-conical longitudinal section, suitable for making-up inside the box element;
c) a shoulder, orthogonal to the axis of the pipe, positioned on the pin element, half-way along the thread;
d) a shoulder, orthogonal to the axis of the pipe, positioned half-way along the thread of the box element and suitable for mating with the shoulder of the pin element when the connection is made-up;
e) two insets machined at the beginning and at the end of the box element respectively, suitable for interfering with corresponding flares machined at the beginning and at the end of the pin element; characterized in that:
f) between the flare and beginning of the thread of the pin element there is an annular slot, the depth of which (allowing the thread to be machined) is recovered with a corresponding shoulder, having a thickness substantially equal to the depth of said slot, at the end of the thread;
g) between the initial inset of the box element and beginning of the corresponding thread, there is another annular slot, similar to the first, the depth of which (allowing the thread to be machined) is recovered with a possible corresponding shoulder or is absorbed in the inset at the end of the thread.
According to the present invention, it is therefore possible to obtain an integral joint, with at least two shoulders, having a slight increase in the external diameter (2-3%) in correspondence with the joint itself, whose geometry consequently remains identical to that of the pipes to be connected. In fact, due to the presence of the two slots, which can have a length ranging from 1 to 2 cm and a depth of 2-4 mm, depending on the diameter and thickness of the pipe, the threads start from the portion of the pipe with the lower thickness so that, at the end of the thread, the thickness of the slot itself is recovered by the shoulders. In this way, at least one extra shoulder can be obtained at the end of the joint, without having to increase the thickness of the terminal portions of the pipes to be connected.